Hydrostatic conveyor drive

Abstract

A conveyor drive system employing a constant speed master drive and a slave drive of the hydrostatic, closed loop type in which there are no electrical or hydraulic feedback lines between the master and slave drive unit. The master drive moves the conveyor at a constant speed as load varies and the slave drive unit responds to changes in load on the conveyor to vary the speed of the drive to maintain a constant pull on the conveyor to insure that the slave drive shares its portion of the load with the master drive.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. In a conveyor drive system having a master drive for driving the conveyor at a constant speed independent of conveyor load, a slave drive system connected to said conveyor independently of said master drive for moving said conveyor in the same direction, said slave drive system including a closed circuit hydrostatic drive having a variable displacement pump delivering fluid in a supply line to a fixed displacement motor, control means for varying the displacement of said pump including a control member movable in one direction to increase the displacement and in the other direction to decrease the displacement of said pump, first means biasing said control member in said one direction with a uniform force, and second means connected to said control member to move the latter in said other direction to decrease the displacement of said pump and the speed of said motor in proportion to the pressure in said supply line. 
     
     
       2. The combination of claim 1 in which said first means includes a hydraulic cylinder connected to a source of constant pressure for movement in said one direction. 
     
     
       3. The combination of claim 2 in which said source of constant pressure is a fixed displacement pump forming part of the slave drive system. 
     
     
       4. The combination of claim 1 in which said second means includes a hydraulic actuator having a piston and a conduit communicating said actuator at one side of said piston with said supply line. 
     
     
       5. The combination of claim 4 and further comprising a sequence valve disposed in said conduit and being manually adjustable to open at a selected pressure level higher than the pressure of said constant source of pressure. 
     
     
       6. The combination of claim 1 and further comprising means for adjustably limiting the range of movement of said control member to determine the maximum and minimum displacement of said pump. 
     
     
       7. The combination of claim 1 and further comprising a hydraulic cylinder for moving said control member, said first means biasing said control member in one direction including a source of constant pressure communicating with one end of said hydraulic actuator, and said second means biasing said control member in the opposite direction comprising a conduit in communication with said supply line at the upstream side of said motor. 
     
     
       8. The combination of claim 7 and further comprising a sequence valve disposed in a line communicating with the upstream side of said motor and with said hydraulic actuator whereby pressure is delivered to said hydraulic actuator when the pressure at said upstream side is in excess of the constant pressure acting at the other end of said hydraulic actuator. 
     
     
       9. The combination of claim 8 and further comprising a variable orifice disposed between said sequence valve and said hydraulic cylinder for adjustably controlling the speed of movement of said hydraulic cylinder in said one direction. 
     
     
       10. The combination of claim 8 and further comprising a variable orifice between said source of constant pressure and said hydraulic actuator for controlling the speed of said hydraulic actuator in said other direction. 
     
     
       11. The combination of claim 1 and further comprising a four-way reversing valve disposed between said pump and said motor and being movable to select the direction of rotation of said motor. 
     
     
       12. A conveyor drive system for maintaining a constant pull on a conveyor independently of load on the conveyor comprising, a closed circuit hydrostatic drive having a variable displacement pump, a fixed displacement motor connected to the conveyor, a supply line for delivering hydraulic fluid from said pump to said motor, a return line for delivering hydraulic fluid from said motor to said pump, control means movable to vary the displacement of said pump, actuating means connected to said control means to move the latter in proportion to the pressure in said supply line to vary the delivery of hydraulic fluid from said pump to said motor to vary the speed of said motor, said actuating means comprising a hydraulic cylinder, means biasing said cylinder in one direction with a constant force, and a fluid conduit communicating said cylinder with said supply line for moving said cylinder in the other direction in response to pressure in said supply line. 
     
     
       13. The combination of claim 12 and in which said actuating means includes a linear actuator having one end in fluid communicating with said supply line and the other end connected to a source of constant pressure, said source of constant pressure being operable to bias said actuating means in a direction increasing the speed of said motor and said cylinder being movable in the other direction to decrease the speed of said motor. 
     
     
       14. The combination of claim 12 in which said means biasing said cylinder with a constant force includes a source of pressure maintained at a constant level, said source of pressure communicating with said cylinder to urge the latter in said one direction. 
     
     
       15. The combination of claim 14 in which said constant source of pressure includes a charging circuit communicating with said supply and return lines to maintain the latter charge at a minimum pressure level. 
     
     
       16. The combination of claim 14 and further comprising a variable orifice disposed in said fluid conduit and a second variable orifice between said fluid cylinder and said constant source of pressure for adjustably controlling the speed of movement of said cylinder. 
     
     
       17. The combination of claim 12 and further comprising a reversing valve interposed in said supply and return lines between said pump and said motor and being movable to reverse the direction of said motor. 
     
     
       18. The combination of claim 12 and further comprising a sequence valve disposed in said fluid conduit and being manually adjustable to open at a pressure level to exert a force in excess of and in opposition to said constant force.